A black hole emits no light from inside its event horizon. The bright activity associated with black holes usually comes from matter outside that boundary.
When gas falls toward an actively feeding black hole, it can form a hot accretion disk and release enormous amounts of radiation before crossing the horizon.
Black holes come in different scales
Stellar-mass black holes can form when massive stars collapse. Supermassive black holes, containing millions or billions of solar masses, occupy the centers of most large galaxies.
Astronomers are still investigating how supermassive black holes formed and grew so rapidly in the early universe.
A black hole’s gravity is not unusually aggressive at large distances. If the Sun were replaced by an object with the same mass, Earth’s orbit would remain approximately the same—although the loss of sunlight would make the planet uninhabitable.
Why active black holes can be bright
Material in an accretion disk is compressed and heated as it moves inward. This environment can emit radiation across multiple wavelengths.
Some systems also produce narrow jets of particles moving close to the speed of light. The jets originate in the region around the black hole and disk, not from inside the event horizon.
Quasars are exceptionally luminous active galactic nuclei powered by rapidly accreting supermassive black holes.
Feedback can change a galaxy
Radiation, winds and jets from an active galactic nucleus can heat gas or push it away from a galaxy’s central regions. This may reduce the cold gas available for new stars.
Under other conditions, compression can contribute to star formation. Black-hole feedback is therefore complex, and astronomers continue studying when it suppresses or encourages stellar growth.
What black-hole images actually show
The Event Horizon Telescope images of M87* and Sagittarius A* do not show the black holes themselves. They show bright emission surrounding a dark central region known as the shadow, whose appearance is shaped by gravity and the event horizon.
Black holes influence galaxies through gravity and through the energy released by nearby matter. The most visible effects occur outside the darkness.
Sources
- NASA Black Holes overview: https://science.nasa.gov/universe/black-holes/
- NASA anatomy of a black hole: https://science.nasa.gov/universe/black-holes/anatomy/
- NASA active-galaxy guide: https://imagine.gsfc.nasa.gov/science/objects/active_galaxies1.html
- Event Horizon Telescope: https://eventhorizontelescope.org/